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Careful control of synthetic conditions can enhance the structural diversity of metal–organic frameworks (MOFs) within individual metal-linker combinations. Herein, we show that hcp topology MOFs of both Zr(IV) and Hf(IV), linked by the extended (ethyne-1,2-diyl)dibenzoate linker, can be prepared by modulated self-assembly. The controlled addition of acetic acid and water to solvothermal syntheses is essential to generate these phase pure hcp topology materials, which are characterised experimentally and computationally. The central alkyne unit of the linker can be quantitatively brominated, but this results in partial degradation of the hcp phase, in contrast to the more stable fcu topology analogues. Nevertheless, the MOFs represent new members of the hcp topology isoreticular series showing high crystallinity and porosity, and demonstrate that new materials can be discovered in existing MOF phase spaces through judicious adjustment of key synthetic parameters. [ABSTRACT FROM AUTHOR]